1. Field of the Invention
The present invention relates to a resolution device for semiconductor thin films, more particularly, to a semiconductor thin film resolution device for preparing samples, that are scarcely contaminated by the decomposition reagents or the surrounds, to be used in analyzing ultratrace amounts of impurities in semiconductor thin films.
2. Description of the Prior Art
Semiconductor films such as SiO.sub.2 film or Si.sub.3 N.sub.4 film have been used as a partial diffusion masking for doping reagents or a protective film for sputtered metallic films in silicon semiconductors. When there are contained in the film impurities like Na, K, or Fe, the electrical characteristics of the semiconductor are affected significantly even if the amount may be extremely minute. For this reason, it is necessary to suppress the amount of these impurities to the lowest level possible in order to enhance the capabilities of the semiconductors such as in a Giant Scale Integration. To accomplish such a goal, it is necessary to be able to measure accurately the concentration of impurities in semiconductor films.
For measuring impurities in semiconductor films, the flameless atomic absorption spectrophotometer has been used in the past. Measurements are taken by placing the semiconductor film samples for flameless atomic absorption spectrophotometry on the flameless atomic absorption spectrophotometer. However, there exists a serious problem in the preparation of samples for spectrophotometry.
Namely, according to the prior art method of preparing samples, a semiconductor film is soaked in a mixture of hydrofluoric acid and sulfuric acid, and after direct decomposition, the dissolved solution obtained is evaporated and dried to obtain the residues. Samples for flameless atomic absorption spectroanalysis are obtained by diluting the residues to a predetermined volume with pure water. However, in this prior art method, contamination by the reagent used for resolving the semiconductor sample is exceedingly large. For example, even when reagents refined by the sub-boiling distillation method or the ion exchange method are used, these reagents already contain impurities (Na, K, and the like) in excess of 0.1 ppb so that it has been extremely difficult to accurately measure the amount of impurities in a semiconductor film of less than 10.sup.-10 g/cm.sup.2 by means of flameless atomic absorption spectrophotometry.